The present invention relates to a drill pipe, a method of forming drill pipe and drill pipe formed thereby as well as to a method of reconditioning drill pipe formed by conventional methods.
Some currently available torque and drag reducing tools used in drilling applications installed directly onto drill pipes. Such tools may rotate about the drill pipe to reduce rotational torque. As the outer surface of standard drill pipe is neither perfectly round nor smooth, such tools have compromised torque reduction performance. Additionally, the fluid film operational principle of such tools sees drilling fluid, containing abrasive drill cuttings, passing between the tool and the drill pipe. This creates wear on the drill pipe and may compromise the strength of the drill pipe, particularly as the wear patterns can be deep circumferential grooves which may act as stress raisers in the tubular wall.
The object of the present invention is to provide a drill pipe having an integrally formed journal area having improved hardness, roundness and smoothness and methods of forming a journal on a drill pipe, or to at least provide the public with a useful choice.
According to a first aspect of the invention there is provided a drill pipe having coupling sections at either end thereof:
a pair of stop collars integrally formed with the drill pipe and extending radially outward; and
wherein a hardfacing material has been applied to the outer surface of the drill pipe between the stop collars to form a journal for supporting a rotating tool.
According to a further aspect of the invention there is provided a set of drill pipes as hereinbefore described wherein the stop collars of the drill pipes are located at different positions along the drill pipes to facilitate efficient stacking of the drill pipes.
According to a further aspect of the invention there is provided a combination comprising a drill pipe as hereinbefore described and a drilling tool. The length of the journal is sufficiently longer than the length of the drilling tool to facilitate lubrication and cooling of the interface between the journal and the tool to reduce friction therebetween.
According to another aspect of the invention there is provided a method of forming a journal on a drill pipe during manufacture comprising the steps of:
i/ applying a hardfacing material to a section of the drill pipe between a pair of intregally formed stop collars prior to heat treating the drill pipe,
ii/ heat treating the drill pipe; and
iii/ precision grinding the section to which the hardfacing material has been applied to form a smooth journal surface on the drill pipe.
The hardfacing is preferably an amorphous type hardfacing. The hardfacing may be applied by high velocity oxy fuel, plasma spray, combustion powder, combustion wire, arc wire spraying, flame thermal spray, nitriding, carburising or other case hardening techniques. Alternatively, the hardfacing may be a ceramic material or PDC (polycrystalline diamond compact).
According to another aspect of the invention there is provided a method of forming a journal on a section of preformed drill pipe comprising:
i/ lightly machining a section of the drill pipe between a pair of intregrally formed stop collars;
ii/ applying a hardfacing material to the section of the drill pipe; and
iii/ grinding the hardfaced section so that it is round and smooth.
The hardfacing material is preferably applied by spluttering, for example by twin arc or high velocity oxy fuel spraying the hardfacing material directly onto the existing drill pipe. The hardfacing material is preferably ARMORCOR M or ARNCO with options being Rolls Wood or other suitable materials.
There is further provided a drill pipe having coupling sections at either end thereof and a journal formed on the drill pipe between said coupling sections, the ovality of the journal being less than or equal to 0.7 mm.